Thursday, May 23, 2013
CPAP vs BiPAP in NMD
I have written before about having hypoventilation at night due to an underlying mitochondrial myopathy. I had a sleep titration study and was placed on a CPAP instead of a BiPAP. I did question the technician about this, as literature I have read has said BiPAP, not CPAP, should be used in persons with NMD (Neuromuscular Disease) and respiratory muscle weakness as I have. He said they have to start out on the CPAP first.
I received a call yesterday from the home health company who will be setting up my machine. They said my doctor had ordered a CPAP machine. I already have a BiPAP machine that I had gotten 3 years ago, but had difficulty tolerating (no sleep study or titration with that, just pressures picked by a former doctor). I explained this to them, but they said I would have to purchase this CPAP machine.
My question is: I am really uncomfortable with getting the CPAP if this potentially could make things worse for me in the long run. Am I making too much of the CPAP vs. BiPAP issue? I have put 2 calls into my doctor (who is a sleep specialist), but have had no response as of yet. I am not sure what to do at this point. Can you help me? Thanks.
There are two types of sleep apnea: obstructive and central. Obstructive sleep apnea (OSA) is more common type and it occurs when the back of the throat relaxes during sleep leading to airway collapse and lack of air flow. Causes of worsening of collapse include obesity, large tonsils, large tongue, and abnormal jaw anatomy or nasal anatomy. Occasionally, weak upper airway muscles (in the back of the throat) may be contributing to the airway collapse and thus the sleep apnea. Loud snoring often accompanies this type of sleep apnea.
Central sleep apnea (CSA) is less common. In CSA, there is lack of effort to breathe during sleep as the brain fails to send the signal to the muscles of respiration, or if the muscles cannot respond to the signals due to neuromuscular disease (NMD).
Several factors determine the effect of NMD on sleep and on sleep disordered breathing. Weakness of the respiratory muscles, weakness of the muscles of the back of the throat, or a decrease in respiratory drive (the signal from the brain to breath) can result in OSA/CSA or a combination of the two.
The usual treatment for OSA is using a continuous positive airway pressure (CPAP) device. Since OSA has been reported in patients with NMD, it is not unreasonable to use this modality when a sleep study indicates the presence of an obstructive component during sleep. If CPAP does not optimally control the sleep disorder and/or hypoventilation (if present), then a trial of bi-level positive airway pressure (BiPAP®) or variable pressure support (VPAP®) may be attempted.
The way CPAP may help control sleep apnea in NMD is twofold. Sometimes, muscle weakness in the back of the throat causes upper airway collapse during sleep. This may be reversed with CPAP. Also, the chest wall and diaphragm in NMD become mechanically disadvantaged during supine sleep due to the upward pressure exerted by the abdominal contents. CPAP may help stabilize the chest wall and help in the downward movement of the diaphragm during inhalation, which results in an improvement of respiratory status during sleep. So it's possible that CPAP may be of benefit in NMD patients with OSA.
It is true that CPAP is cheaper than other treatment modalities and therefore, insurance companies often insist on testing this treatment option before proceeding with others. There are specific guidelines from the government regarding the use of BiPAP in patients with NMD. They state that BiPAP can be approved if hypoventilation is present and there is no OSA or, if OSA is present, the patient has to first "fail" CPAP. It is possible that this latter guideline may be the situation in your case. In other words, you have to "fail" CPAP before they can get BiPAP approved for you. But, as detailed above, CPAP may be adequate in the treatment of some individuals with NMD, and therefore should be tested. As you may have any combination of OSA/CSA, the results of your sleep study and your titration study should be explained to you in detail by your doctor, as well as the rationale for choosing CPAP as your initial treatment.
Now, I would like to address a technical issue. BiPAP machines are capable of functioning exactly like (or very closely to) CPAP machines. You already own a BiPAP machine and that machine should be adjustable in a sufficient way to meet your needs, without the need to buy a new CPAP machine. I suspect that your home care company wants you to purchase (or rent) a CPAP machine because they cannot offer service for a machine that they did not sell (or rent) to you. This could be a financially or a technically driven decision. Obviously, I am not aware of the details, but this is something you should consider. I believe that most new machines are easy to adjust. You may be able to take your current BiPAP to a Sleep Specialist or Sleep Technician, and he/she can set it and test it to fit your needs if they have the right equipment and technical knowledge.
With this, I hope my note is helpful, and the discussion with your Sleep Specialist proves to be reassuring.
Ziad Shaman, MD
Assistant Professor of Medicine
School of Medicine
Case Western Reserve University